1. Field of the Invention
The invention pertains to blow molding apparatus such as used to blow mold beverage containers and the like utilizing shear plates or steels to sever the neck of the blown product, the shear plates being in the form of segments mounted upon displaceable top plates movable toward each other.
2. Description of the Related Art
Blow molding apparatus is widely used to economically form synthetic plastic containers such as those used in the sale of milk, soft drinks, cleaning liquids, etc. In such molding processes, a heated parison is inserted into the mold, subjected to internal compressed air which forces the thermoplastic material into engagement with the mold walls to assume the configuration of the mold, and after forming, the blow pin is raised to shear the bottle neck to produce a finished product having an accurately squared neck end for receiving a cap or lid.
The mold top plates, usually two in number, are slidably supported so that they may be moved toward and away from each other to release the finished product. The top plates each support a shear steel holder which, in turn, supports arcuate shear plates or steels having sharpened inner edges. The top plates, shear steel holders and shear plates are usually each of a 180.degree. configuration wherein opposed like components will define a complete circumferential configuration when the two top plates are moved together. Within the neck defined by the shear plate holders, the blow pin end received within the blown product cooperates with the shear plates wherein the product is pinched or sheared off by the shear plates when the blow pin is raised. This shearing off of the product neck defines a clean neck edge at the bottle opening wherein caps or lids may be applied to the bottle opening, as designed.
Blow molding apparatus forming beverage containers operates at high speeds at hundreds of cycles per hour, and although the blown thermoplastic material is soft, repeated engagement with the shear steels or plates wears and dulls the shear plates resulting in uneven, fuzzy, burred and torn container edges, and it is necessary to periodically replace the shear plates within their associated holders due to shear plate wear.
There is a need for a quick adjustment of worn shear plates, but prior to the introduction of the instant invention, practical blow molding apparatus having adjustable shear plates has not been commercially available.